scholarly journals Spontaneous mutations and the origin and maintenance of quantitative genetic variation

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Wen Huang ◽  
Richard F Lyman ◽  
Rachel A Lyman ◽  
Mary Anna Carbone ◽  
Susan T Harbison ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Quantitative Traits ◽  
Spontaneous Mutation ◽  
Natural Populations ◽  
Empirical Work ◽  
Stabilizing Selection ◽  
Spontaneous Mutation Rate ◽  
Evolutionary Forces ◽  
Quantitative Genetic

Mutation and natural selection shape the genetic variation in natural populations. Here, we directly estimated the spontaneous mutation rate by sequencing new Drosophila mutation accumulation lines maintained with minimal natural selection. We inferred strong stabilizing natural selection on quantitative traits because genetic variation among wild-derived inbred lines was much lower than predicted from a neutral model and the mutational effects were much larger than allelic effects of standing polymorphisms. Stabilizing selection could act directly on the traits, or indirectly from pleiotropic effects on fitness. However, our data are not consistent with simple models of mutation-stabilizing selection balance; therefore, further empirical work is needed to assess the balance of evolutionary forces responsible for quantitative genetic variation.

scholarly journals Extreme climatic events but not environmental heterogeneity shape within-population genetic variation in maritime pine

2021 ◽  
Author(s):  
Juliette Archambeau ◽  
Marta Benito Garzón ◽  
Marina de Miguel Vega ◽  
Benjamin Brachi ◽  
Frédéric Barraquand ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Population Genetic ◽  
Environmental Heterogeneity ◽  
Maritime Pine ◽  
Heterogeneous Environments ◽  
Evolutionary Forces ◽  
Common Gardens ◽  
Quantitative Genetic ◽  
Population Genetic Variation

AbstractHow evolutionary forces interact to maintain quantitative genetic variation within populations has been a matter of extensive theoretical debates. While mutation and migration increase genetic variation, natural selection and genetic drift are expected to deplete it. To date, levels of genetic variation observed in natural populations are hard to predict without accounting for other processes, such as balancing selection in heterogeneous environments. We aimed to empirically test three hypotheses: (i) admixed populations have higher quantitative genetic variation due to introgression from other gene pools, (ii) quantitative genetic variation is lower in populations from harsher environments (i.e. experiencing stronger selection), and (iii) quantitative genetic variation is higher in populations from spatially heterogeneous environments. We used phenotypic measurements of five growth, phenological and functional traits from three clonal common gardens, consisting of 523 clones from 33 populations of maritime pine (Pinus pinaster Aiton). Populations from harsher climates (mainly colder areas) showed lower genetic variation for height in the three common gardens. Surprisingly, we did not find any association between within-population genetic variation and environmental heterogeneity or population admixture for any trait. Our results suggest a predominant role of natural selection in driving within-population genetic variation, and therefore indirectly their adaptive potential.

Maintenance of Quantitative Genetic Variation

2018 ◽  
Author(s):  
Bruce Walsh ◽  
Michael Lynch
Keyword(s):  
Genetic Variation ◽  
Quantitative Genetics ◽  
Stabilizing Selection ◽  
Quantitative Genetic ◽  
Wide Range

One of the major unresolved issues in quantitative genetics is what accounts for the amount of standing genetic variation in traits. A wide range of models, all reviewed in this chapter, have been proposed, but none fit the data, either giving too much variation or too little apparent stabilizing selection.

scholarly journals Cryptic variation and its manifestation in the Lower Trentonian Rafinesquina lineage (Ordovician, New York State)

1992 ◽  
Vol 6 ◽  
pp. 292-292
Author(s):  
Robert Titus
Keyword(s):  
New York ◽  
Genetic Variation ◽  
Natural Selection ◽  
New York State ◽  
Ecological Factors ◽  
Stabilizing Selection ◽  
Rapid Population Growth ◽  
York State ◽  
Cryptic Variation ◽  
Adaptive Peak

Species populations commonly carry a great deal of genetic variation which is not expressed in individual phenotypes. Cryptic variation can be carried in recessive alleles, in cases of heterosis, or where modifier genes inhibit expression of the hidden trait. Other genetic and ecological factors also allow cryptic variation. Stabilizing selection prevents the expression of hidden traits; normalizing selection weeds out the deviants and canalizing selection suppresses their traits. Together the two keep the species near the top of the adaptive peak. Cryptic variation balances a species' need to be well-adapted to its environment and also for it to maintain a reserve of variation for potential environmental change. Expression of cryptic traits is rare and is usually associated with times of greatly reduced natural selection and rapid population growth, when the lower slopes of the adaptive peak are exposed.A possible example of the manifestation of cryptic traits occurs within the lower Trentonian Rafinesquina lineage of New York State. The two most commonly reported species of the genus have been reappraised in terms of cryptic variation. Extensive collections of Rafinesquina “lennoxensis” reveal far more intergrading morphotypes than had hitherto been recognized. The form which Salmon (1942) described is broadly U-shaped with sulcate margins. It grades into very convex forms as well as sharply-defined or convexly geniculate types. Of great importance, all forms grade into the flat, U-shaped, alate R. trentonensis, which is, by far, the most common and widespread lower Trentonian member of the genus. The R. “lennoxensis” assemblage has a very narrow biostratigraphy, being confined to a few locations in the upper Napanee Limestone. This places it in a quiet, protected, low stress, lagoonal setting behind the barrier shoal facies of the Kings Falls Limestone.The R. “lennoxensis” assemblage does not constitute a natural biologic species; it is reinterpreted as an assemblage of phenodeviants occupying a low stress, low natural selection lagoon facies. All such forms should be included within R. trentonensis. Given the evolutionary plasticity of this genus, extensive cryptic variation is not surprising.

scholarly journals Evidence Concerning the Inadequacy of Mutation as an Explanation of the Frequency of the Sickle Cell Gene in the Belgian Congo

Blood ◽  
1955 ◽  
Vol 10 (4) ◽  
pp. 341-350 ◽  
Author(s):  
J. M. VANDEPITTE ◽  
WOLF W. ZUELZER ◽  
JAMES V. NEEL ◽  
J. COLAERT
Keyword(s):  
Natural Selection ◽  
Sickle Cell ◽  
Spontaneous Mutation ◽  
Genetic Modifier ◽  
Paper Electrophoresis ◽  
Preliminary Calculation ◽  
Spontaneous Mutation Rate ◽  
Balanced Polymorphism ◽  
Belgian Congo ◽  
Cell Gene

Abstract It is pointed out that there are two outstanding (and not mutually exclusive) possible explanations for the persistence of the sickle cell gene in the face of strong negative natural selection. These are (1) "balanced polymorphism," and (2) a high spontaneous mutation rate. In Léopoldville, Belgian Congo, approximately 25 per cent of the natives exhibit the sickling phenomenon. Over a two and one-half year period 261 patients with sickle cell disease, distributed among 243 families, were seen at the Institute of Tropical Medicine in Léopoldville. A total of 233 of the 243 mothers of the patients in this series was tested for the sickling phenomenon. Only two failed to sickle. Hemoglobin from these two women was normal on paper electrophoresis. The occurrence of these two exceptional mothers can be explained on the basis of mutation at some stage of oogenesis resulting in a sickle cell gene. Alternate possible explanations include (1) transmission by the mother of some other abnormal gene affecting hemoglobin synthesis, (2) occurrence in the mother of a genetic modifier of the effects of the sickle cell gene, (or its normal allele), and (3) unreported adoption. These data make possible a preliminary calculation of the extent to which mutation may be responsible for maintaining the sickle cell gene. Calculations based on the assumption that both these exceptional mothers indicate the occurrence of a mutation will lead to maximal estimates of the rate of mutation of the sickle cell gene. This maximal estimate is 1.7 x 10-3 per gene per generation. This rate, although very high by the usual standards of human mutation rates, is only approximately one-tenth that necessary to offset natural selection in a population with 25 per cent sickling.

scholarly journals Quantitative genetic variation of enzyme activities in natural populations of Drosophila melanogaster

1980 ◽  
Vol 77 (2) ◽  
pp. 1073-1077 ◽  
Author(s):  
C. C. Laurie-Ahlberg ◽  
G. Maroni ◽  
G. C. Bewley ◽  
J. C. Lucchesi ◽  
B. S. Weir
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Variation ◽  
Enzyme Activities ◽  
Natural Populations ◽  
Quantitative Genetic

scholarly journals Spontaneous mutation rate of modifiers of metabolism in Drosophila.

Genetics ◽  
1995 ◽  
Vol 139 (2) ◽  
pp. 767-779 ◽  
Author(s):  
A G Clark ◽  
L Wang ◽  
T Hulleberg
Keyword(s):  
Spontaneous Mutation ◽  
Balance Model ◽  
Environmental Variance ◽  
Spontaneous Mutation Rate ◽  
Empirical Estimates ◽  
Quantitative Genetic ◽  
Rate Of Increase ◽  
Rigorous Test ◽  
Quantitative Genetic Parameters ◽  
New Mutations

Abstract A rigorous test of our understanding of evolutionary quantitative genetics would be to predict accurately the equilibrium distribution of a character from empirical estimates of the relevant parameters in a mutation-selection-drift balance model. An aspect of this problem that is amenable to experimental analysis is the distribution of the effects of new mutations. This study quantifies the divergence among 200 lines of Drosophila melanogaster as they accumulated mutations on the second chromosome and estimates the rate of increase of variation and covariation in metabolic characters. Amounts of stored triacylglycerol and glycogen and the activities of a series of 12 metabolic enzymes were assayed in a subset of lines at generations 0, 11, 22, 33 and 44. Analyses of the rate of increase in the among-line variance in each trait allowed estimation of Vm/Ve, the ratio of among-line variance added per generation to the environmental variance. Values of Vm/Ve for the second chromosome ranged from 0.0004 to 0.0289 per generation. Six of the 16 characters showed significant departure from a normal distribution, and several lines exhibited large changes in more than one character. The covariance of pairs of traits also was partitioned into a within-line component (environmental covariance, Cov(e)) and an among-line component (mutational covariance, Covm). Both variances and covariance among lines increased over time, as assessed by linear regression, whereas environmental covariance showed no such trend. Results indicate that the quantitative genetic parameters describing the variation in metabolic traits are similar to those of other continuous characters.

Interchange polymorphism in natural populations of Allium paniculatum L. (Liliaceae): nature, frequency, effects, and mechanism of maintenance

1986 ◽  
Vol 28 (3) ◽  
pp. 348-357 ◽  
Author(s):  
R. Lozano ◽  
C. Ruiz Rejón ◽  
M. Ruiz Rejón
Keyword(s):  
Chiasma Frequency ◽  
Vegetative Reproduction ◽  
Spontaneous Mutation ◽  
Natural Populations ◽  
Egg Cell ◽  
Satellite Chromosome ◽  
Spontaneous Mutation Rate ◽  
Selection Equilibrium ◽  
Nature Frequency ◽  
Reproductive Characters

A reciprocal translocation was found with a high frequency (average 44.44%) in four natural populations of Allium paniculatum L. (Liliaceae) from the South of Spain. The chromosomes involved are 1 and 7. The translocation is reciprocal and unequal. Chiasma frequency in the chromosomes not involved in the interchange is not affected, but chiasma frequency is decreased in the translocated chromosomes in the heterozygotes. As a satellite chromosome is involved in the interchange, the nucleolus is associated with the quadrivalent and the pattern of nucleolus formation is changed in heterozygotes, which have a lower mean number of nucleoli [Formula: see text] than homozygous standard individuals [Formula: see text]. The spontaneous mutation rate for interchanges during the early stages of microsporogenesis is high (μ = 1.08 × 10−2). No interchange homozygotes were found in any of the four populations analyzed. Furthermore, a comparative analysis of heterozygous (HT) and homozygous standard (HM) individuals in two populations demonstrated that homozygous standard plants show, on the whole, higher fitness than the heterozygotes. This can be attributed to a greater egg cell fertility and seed set. The possible causes of maintenance are discussed: the interchange in A. paniculatum is probably not maintained by overdominance for generative reproductive characters, nor by a mutation–selection equilibrium. One possibility, that heterozygotes have superior vegetative reproduction, still remains open for future investigation.Key words: Allium paniculatum, interchange polymorphism, fitness.

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